Automatic volume control arrangement



Nov. 14, 1950 L. w. COUILLARD 2,530,000

AUTOMATIC VOLUME comm. ARRANGEMENT Filegi Nov. 1. 1945 as OUITPUT 107%14 Cozn'LLARD IN VEN TOR.

ATTaR/YE Y Patented Nov. 14, 1950 AUTOMATIC VOLUME CONTROL ARRANGEMENTLuther W. Couillard, Cedar Rapids, Iowa assignor to Collins RadioCompany, Cedar Rapids, Iowa,

a corporation of Iowa Application November 1, 1945, Serial No. 626,145

6 Claims.

This invention relates to electric wave transmission systems and moreespecially to arrangements for automatically maintaining the outputlevel of such systems uniform.

Aprincipal object of the invention is to provide an improved automaticoutput volume control circuit arrangement for radio receivers and thelike.

Another object is to provide an automatic output level regulatingarrangement wherein the ratio of the level regulating voltage to levelchange is very high.

A feature of the invention relates to an automatic volume controlarrangement employing a special regulator tube whose output voltage forA. V. C. purposes is a function of the level of the A. C. component ofthe modulated carrier wave input level, as well as a function of a levelof the rectified carrier wave.

Another feature relates to an automatic volume control arrangementwherein the A. V. C. volt-. age is derived from a grid-controlledamplifier tube whose input electrodes are driven by a portion of therectified carrier wave, and whose plate or anode is driven by thecarrier wave before rectification.

A further feature relates to a cathode driven A. V. C. regulator tubewhich derives its plate potential from the carrier wave whose outputlevel is to be regulated.

A further feature relates to an automatic volume control arrangementemploying the combination of a diode rectifier detector, and agridcontrolled tube of the sharp plate current cutofi and highamplification factor, and. with its control grid at D. C. groundpotential.

A still further feature relates to the novel organization, arrangementand interconnection of parts which cooperate to provide an improvedautomatic volume control or output level control device.

, Other features and advantages not specifically enumerated, will beapparent after a consideration of the following detailed descriptionsand the appended claims. 1

Inasmuch as the invention is primarily concerned with the A. V. C.regulating arrangement of a wave signalling system, only those parts ofa conventional radio receiver are illustrated so as to enable theinventive concept to be understood for purposes of practical use.Furthermore, while the invention is disclosed specifically in connectionwith a radio receiver, it will be understood that the fundamentalfeatures of the invention are equally well applicable to transmitters,repeaters, and the like.

In the drawing,

Fig. l is a schematic circuit diagram of a radio receiving systemembodying the invention.

Fig. 2 is a graph showing the relation between input carrier voltage andoutput signal level of the system of Fig. 1.

Referring to Fig. 1, there is shown a typical high frequency wavesignalling arrangement in the form of a conventional radio receiver ofthe superheterodyne type. It will be understood however that theinvention is not limited to a superheterodyne receiver but can also beapplied to so-called tuned radio frequency receivers. The receiver shownin Fig. 1 comprises a radio frequency amplifier unit I, anoscillator-mixer unit 2, an intermediate frequency amplifier unit 3, anintermediate frequency coupling transformer 4, a detector 5, and anaudio frequency amplifierunit 6. If the receiver is of the type havingmore than one intermediate frequency stage, the trans-' former 4 may bethat associated with the output of the last intermediate frequenc stagewhich feeds the second detector 5. Detector 5 is preferably a vacuumtube rectifier of the type 12H6, the anodes of which are connectedtogether and to one terminal of the secondary winding of transformer 4.This secondary winding, like the primary winding, is tuned to thedesired carrier or intermediate frequency of the system. The secondarywinding is returned through the recti fier load resistor 1 to thecathode 8 of the rectifier. Resistor 1 may be of approximately 300,000

ohms and is shunted by a condenser 9 of ap-. proximately 300 mmfd. forby-passing any high' frequency or intermediate frequency currents. Thecathode 8 is normally positively biassed with respect to ground by meansof voltage divider re-: The terminal [2 of resistor H, is connected topositive D. C. voltage of a'pproximately 200 volts while oneend of theresistor 10; is grounded. The cathode 8 is connected to the; Resistor l0may be of approximately 10,000 ohms, while the resistor H may beapproximately 100,000: Under these circumstances, cathode 8 is. normallypositively biassed above ground to ap,.- proximately 20 volts D. C.Resistor I0 is prosistors I0, .I I.

junction point of resistors I0 and II.

ohms.

Tube 14 is any well-known type of grid-comtrolled vacuum tube having asharp plate current cutoff characteristic and with a high amplifica-:,

tion factor, of which the type 12SJ'7 is representative. Preferably tubeI4 is of the triple grid type and has its cathode I5 driven undercontrol of the D. C. potential variations at the point I6 and with itscontrol grid H at D. 0. ground potential through resistor I8 which maybe approximately 220,000 ohms. The second grid [9 is connected directlyto the anode '20, while the suppressor grid 2! is connected directly tothe cathode I5. A condenser 22 of approximately .01 mfd. is connecteddirectly across grid IT and cathode I5, so as to maintain them at thesame audio frequency potential.

Plate electrode 20 and grid I9 are supplied with operating voltagethrough the condenser 23 of approximately 100 mmfd. from the outputterminal 24 of the intermediate frequency amplifier 3. The intermediatefrequency potential which is obtainable at the primary of transformeriis approximately twice that obtainable at the secondary. thereof. Theplate 20 of tube I l isD. C. returned through aresistor 25 ofapproximately 1 megohm. The D. C. voltages developed across resistor 25are applied through resistor 20 of approximately 470,000 ohms tothe A.V. C. conductor 21 which leads to the control grid bias circuit of theradio frequency amplifier tube in stage I, so as to control the gainthereof in the usual A. V. C. manner. Anyaudio frequency componentspresent in the D. C. voltages across resistor 25 are removed by thefilter which is constituted of the resistor 26 and the condenser 28 ofapproximately .1 mfd.

The detected audio frequency signals from the intermediate frequencyamplifier Which appear at the point 56 are fed to the audio frequencyamplifying unit 5 through the coupling condenser 29 Under theabove-described conditions, when no radio frequency signals are appliedto amplifier I, the point I6 is at positive 20 volts D. C. Sincecorresponding to the resultant rectified intermediate frequency carrierand the normal bias on cathode 8,'the tube I4 becomes plate currentconductive. Under these conditions the carrier voltage which is appliedthrough condenser 23 to the plate 20 is rectified and develops acorresponding D. C. voltage across resistor 25. Since tube I4 has a highamplification factor, the change in condition from no plate current tofull plate current can be effected with a change in potential of cathodeI5 of the order of 1 volt D. C. When tube I4 is fully plate'conductive,approximately 40 volts of automatic volume control potential areavailable over conductor 27. Thus it can be seen that if the rectifiedcarrier signal at point I6 changes from an initial value of 20 volts toa value of 21 volts, the automatic volume control voltage which isavailable will be 40 volts D. C. 7

It will also be seen that since the change from a no conductivity tofull conductivity of tube It is controlled both by the undetectedcarrier applied to plate 20 and by the resultant detected signal appliedto cathode I5, the resultant automatic" twice the intermediate frequencyvoltage is available when the tube I4 is connected to the primary of thelast intermediate frequency transformer 4. .Under the values abovementioned, the 40 volts of automatic volume control voltage decreasesthe gain of the radio frequency amplifier I, so that the output of thesystem changes only a very small amount notwithstanding a large increasein modulated carrier signal input to h amplifier l- .An xam nat qnwf tgrap of Fig. 2 shows that with an arrangement suchas shown in Fig. 1 itis possible to maintain the output level of the radio receiver in-.deci]0 els within comparatively narrow limits overa very wide range ofmicrovolts input to the amplifier i. While one particular embodiment hasbeen dis-.- closed in Fig. 1, it will be understood that;.vari ouschanges and modifications may be made therein without departing from thespirit and. Scope of the invention.

What is claimed is: 1. A volume control arrangement for carrier Wavereceiving systems, comprising a carrierwave amplifier, a 'carrier'waverectifier having. circuit connections to. said amplifier forcontinuo'iisly rectifying both weak andfstrong carriers, a load circuitconnected to, said rectifier to develop therein demodulated audiofrequency signal voltages, a single ain control amplifier tube of: thegrid-controlled'ftype, mearisto apply the carrier beforerectification'to th'e'plateof saidjgain' control'amplifiertube so'thatthe operating plate potential thereof is 'der'ivedfsolely from saidcarrier, circuit means connecting said load circuit to theinput ofsai'dgain' control amplifier tube to correspondingly varyithe platecurrent of said tube for 'both'weak and strong carriers. a separate loadcircuit for said gain control amplifier tube for developing 'directcurrent voltages proportionate both'to the'level' of the carrierbeforerectification and to the amplitudes of the demodulated signals from saidrectifier, and'meansfor applying said direct currentvoltages 'to againcontrol element of said carrier wave amplifier;

2. A volume control arrangement according to claim 1, in which thecarrier wave amplifier is coupled to said rectifier through a trans-'former, and circuit connections are provided between the primary of saidtransformerandthe plate of said gain control amplifier-"tube forsupplying said gain control tube with its operating -plate voltage, saidrectifier having its load circuit in the form of a resistancewhich'is'connected to the cathode of saidgain control" tube to drive said cathodepositively "with respectto its control grids.

3. A volume control arrangement for carrier wave receiving systems,comprising a"c'arrier' Wave amplifier stage, a signal detector coupledto the output of said stage, 'a load circuitfor said detector fordeveloping audio frequency signal "deihodulationsQa "single gain controlamplifier tube of the grid-controlled type, circuit" connections betweenthe said load circuit and the cathode of said gain control amplifiertube for varying the cathode potential of said tube with respect to itscontrol grid in accordance with the said demodulations, and othercircuit connections between the output of said carrier wave amplifierstage and the plate of said gain control amplifier tube whereby saidplate receives its operating voltage solely from said stage prior torectification by said detector, and means for applying the rectifiedplate current of said gain control amplifier tube to control the gain ofsaid amplifier stage.

4. A volume control arrangement according to claim 3, in which saiddetector load circuit includes a load resistance, said gain controlamplifier tube having a sharp plate current cutoff characteristic.

5. A volume control arrangement according to claim 3, in which thecarrier wave amplifier is coupled to said detector through atransformer, said gain control amplifier tube having its plate electrodeconnected to the primary winding of said transformer and its cathodeconnected to the secondary winding of said transformer through saiddetector, and means for maintaining the control grid of said gaincontrol amplifier tube substantially at direct current ground potential.

6. A volume control arrangement for carrier wave receiving systems,comprising means to derive a gain control voltage and including a singleautomatic gain control tube of the gridcontrolled amplifier type havinga single electron-emitting cathode, a single anode and at least oneintervening grid, said means also including a carrier wave amplifierstage and a separate signal modulation detector having an audiofrequency signal developing load circuit, circuit connections betweensaid load circuit and said gain control amplifier tube for normallybiasing said tube to plate current cut-off in the absence of receivedcarrier signals and for biasing said tube to plate conduction for bothstrong and weak received carriers, circuit means for applying the outputof the carrier Wave amplifier stage to the plate of said gain controltube to control the plate current thereof, a load device connected tothe plate of said gain control amplifier tube for developing directcurrent voltages in accordance with the rectified plate current of saidtube, and circuit means for applying said direct current voltages tocontrol the gain of said amplifier stage.

LUTHER W. COUILLARD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,744,718 De Bellescize Jan. 21,1930 1,890,454 Bruce Dec. 13, 1932 1,942,234 Beers Jan. 2, 19341,950,145 Hentschel Mar. 6, 1934 2,034,970 Bond Mar. 24, 1936 2,083,243Schade June 8, 1937 2,135,949 Roberts Nov. 8, 1938 2,144,605 Beers Jan.24, 1939 2,171,677 Weagent Sept. 5, 1939 2,173,248 Braden Sept. 19, 19392,222,759 Burnside Nov. 26, 1940 2,266,509 Percival Dec. 16, 19412,337,196 Hollingsworth Dec. 21, 1943 FOREIGN PATENTS- Number CountryDate 442,506 Germany Apr. 12, 1927

